Heroes usually have the luxury of avoiding consequences, as they go from episode to episode always succeeding. Star Trek II is quite explicitly about how Kirk has avoided consequences for his entire life, starting with him beating the Kobayashi Maru scenario at Starfleet Academy.

David: Lieutenant Saavik was right: You never have faced death.
Kirk: No, not like this. I haven’t faced death. I’ve cheated death. I’ve tricked my way out of death and – patted myself on the back for my ingenuity.

In Star Trek II the consequences all come at once, whether it is a long-forgotten enemy or a son.
And in the end, the ultimate consequence, the death of Spock.

Which, in usual Heroic fashion, turns out to be reversible in Star Trek III: The Search for Spock.

James T. Kirk: [Looking up from the planet surface to see the remains of the Enterprise burning in the atmosphere] My God, Bones, what have I done?
Leonard McCoy: What you had to do, what you always do. Turned death into a fighting chance to live.

And Star Trek II and Star Trek III are about the dialogue between the needs of the many and the needs of the few, or the one.

Sarek: But at what cost? Your ship. Your son.
James T. Kirk: If I hadn’t tried, the cost would have been my soul.

I have to say that Star Trek II & III are rather more elegantly and clearly about these philosophical questions and about the consequences of a lifetime of heroic actions, but these ideas nevertheless are in Infinity War and (presumably) will emerge in Part 2 as well.

In my opinion, there are basically two standout movies from the various phases of the Marvel Cinematic Universe (MCU) so far: the first Captain America (Captain America: The First Avenger) and the first Guardians of the Galaxy. You can watch both as standalone (and in any case Guardians of the Galaxy doesn’t really fit with the Avengers movies anyway). The first Iron Man also has its merits, but suffers from some pretty extensive misogyny. If you watch any Avengers at all, watch Age of Ultron.

In fairness, these movies are a complicated combination of competing factors. I am more interested in the interpersonal dynamics, but for legitimate reasons of fan interest, the movies pretty much have to contain aspects of fan debate and set-piece battles.

Unfortunately one of the main fan debate items, and one which is also cinematically cost-effective, is What happens if character X fights character Y? Which means we end up with a lot of engineered situations of Avenger fighting Avenger.

The set piece battles are similarly popular with fans, but end up basically just being a jumble of people doing super power things until the bad guys inevitably lose.

The MCU is currently broken up into three phases. They have various Avengers, plus Spider-man, but not the X-Men (due to obscure studio licensing issues). The X-Men is a completely separate universe cinematically.

They are basically positioning everyone for the Avengers Infinity War movies (the battle for the Infinity Stones) in 2018 and 2019. That will close a 10 year cycle of movies, I’m not sure where they will go after that.